The present invention relates to ink jet printing onto textiles, to the ink jet printing of wide web, large panel and other extended area substrates, and to the ink jet printing onto large area fabrics and other substrates on a high speed and commercial scale. The invention is particularly applicable to the printing of patterns onto fabric used in quilting such as mattress covers, comforters and bedspreads, and to the printing of signs, banners and other large area substrates. The invention is particularly related to the ink jet printing with ink compositions containing ultra-violet light (UV) curable and other polymerizable or otherwise stable inks.
Needs have arisen for the printing of large banners, flags and signs in quantities that are not economical for many conventional printing processes. Proposals have been made to print such products from electronic source files that can be processed directly on the printing press or printing system, rather than through steps such as film image-setting and plate-making. One such process is that known as ink-jet printing. These processes have been attempted with modest success on surfaces such as vinyl, but printing with success onto textile surfaces has been even more limited. Such processes have been slow and lack reliability. The clogging of print heads in ink jet printing has been too frequent for use in wide width and large area substrates, and the processes used have not produced acceptable printing on textile materials.
Quilting, for example, is an art in which patterns are stitched through a plurality of layers of material over a two-dimensional area of the material. The multiple layers of material normally include at least three layers, one a woven primary or facing sheet that will have a decorative finished quality, one a usually woven backing sheet that may or may not be of a finished quality, and one or more internal layers of thick filler material, usually of randomly oriented fibers. The stitched patterns maintain the physical relationship of the layers of material to each other as well as provide ornamental qualities. Frequently, a combining of stitched patterns with printed patterns is desirable, such as in mattress covers and other quilt manufacture. Producing a printed pattern on a mattress cover requires the application of ink to fabric, which, unlike paper, plastic or other smooth surfaces, presents a texture, third dimension or depth, to the surface on which the printing is applied.
The printing of substrates that are more than several feet, or a meter, wide, referred to as the special category of xe2x80x9cwide widthxe2x80x9d printing, into which category the printing of mattress ticking and most other quiltable materials would fall, is beyond many of the limitations of conventional printing methods. A number of technical problems exist that have deterred the development of the printing of wide fabrics such as mattress covers, upholstery, automobile seat cover fabrics, office partitions and other wide width substrates.
Wide width products are frequently printed in relatively small quantities. Traditional printing typically involves the creation of a plate, a mat, a screen, or some other permanent or at least tangible, physical image from which ink is transferred to the object being printed. Such images contribute a relatively high set up cost that is only economical where the number of identical copies of the product is large. At the other extreme, office printers, for example, print a single copy or a small number of copies of a given document or other item, and are currently of the type that uses no permanent, physical image transfer element, but which rather prints from a software or program controlled electronic image, which can be changed from product to product. Such xe2x80x9csoftxe2x80x9d image printing is sometimes referred to as direct digital printing, although the xe2x80x9csoftxe2x80x9d image need not necessarily be xe2x80x9cdigitalxe2x80x9d in the sense of a set of stored discrete numerical values. Ink jet printers are a common type of such xe2x80x9csoftxe2x80x9d image or digital printers in use today.
Ink jet printers print by projecting drops of ink on demand onto a substrate from one or more nozzles on one or more print heads. Office printers and other narrow width ink jet printers usually dispense water based or other solvent based inks onto the substrate by heating the ink and exploding bubbles of the ink out of the nozzles. These printers are commonly called bubble jet printers. The ink dries by evaporation of the solvent. Sometimes additional heat is used to evaporate the solvent and dry the ink. Printing onto wide width substrates with bubble type ink jet printers, or ink jet printers that use high temperature techniques to propel the ink, severely limits the life of the print head. The heat used to expel the ink and the evaporation of the solvents, particularly during downtime, and the thermal cycling of the heads, causes these print heads to clog or otherwise fail after as little as 20 milliliters of ink is dispensed. Office printers are, for example, often designed so that the print head is replaced every time a reservoir of ink is replenished. For this reason, for larger scale ink jet printing processes, such as wide width printing of films used for outdoor advertising, signage and architectural applications, print heads that use mechanical ink propulsion techniques are more common. Such mechanical print heads include piezo or piezo-crystal print heads, which convert electrical energy into intra-crystal vibrations that cause drops of ink to be ejected from print head nozzles.
Piezo print heads are particularly useful for applying inks that dry by polymerization which can be brought about after the ink leaves the print head and is deposited onto the substrate, usually by exposure to some form of energy medium such as electromagnetic or particle radiation. Inks have been formulated for ink jet printing that can be polymerized by exposure to a radiation curing source such as a focused beam of ultra violet light (UV) or high energy beams of electrons (EB). The inks generally incorporate stabilizers which prevent premature curing due to low levels of light exposure. Therefore, the inks usually require exposure to some threshold level of energy that is necessary to initiate a polymerization reaction. Unless exposed to such threshold energy levels, such inks do not polymerize and remain stable, with a low tendency to dry in the nozzles or elsewhere unless cured by adequate exposure to the energy medium.
Solvent based inks are primarily cured by evaporation of the solvents. Some solvent based inks cure only by air drying, while others require the application of heat to enhance the evaporation of the solvent. In some cases, heat will facilitate a chemical change or polymerization of the ink along with an evaporation of a solvent. Polymerizable inks include monomers and oligomers that polymerize, and other additives. UV curable inks polymerize when exposed to UV light at or above the threshold energy level. These UV curable ink formulations include photoinitiators which absorb light and thereby produce free radicals or cations which induce crosslinking between the unsaturation sites of the monomers, oligomers and polymers, as well as other additive components. Electron beam-cured inks do not require photoinhibitors because the electrons are able to directly initiate crosslinking.
Heat or air curable inks that are organic solvent based or water based inks often do not have as high a color intensity as UV curable or other polymerizable inks because the pigments or dyes that produce the color are somewhat diluted by the solvent. Furthermore, organic solvents can produce an occupational hazard, requiring costly measures be taken to minimize contact of the evaporating solvents by workers and to minimize other risks such as the risks of fire. Solvent based inks, whether applied with heat or not, tend to dry out and eventually clog ink jet nozzles. In addition, solvent based inks set by forming a chemical bond with the substrate, and accordingly, their formulation is substrate material dependent. As a result, the selection of solvent based ink varies from fabric to fabric. Specific ink compositions are paired with specific fabric compositions to improve the fastness of the ink to the fabric, which results from chemical or electrostatic bonds formed between the ink and the fabric. Where the selected ink composition does not react or otherwise has an affinity with the surface of the particular fabric, the ink merely maintains a physical contact with the fabric surface and typically is easily removed by water, another solvent or abrasion. With UV and other radiant beam-curable inks such as electron beam-cured inks, the bonding between the ink and fabric is primarily mechanical and not limited to specific combinations of ink and fabric.
Polymerizable inks, particularly those cured upon exposure to a radiation or energy medium, are difficult to cure on three dimensional substrates such as the surface of a textile. While UV curable inks are capable of providing higher color intensity and do not present the hazards that many solvent based inks present and can avoid nozzle clogging, printing with UV curable ink onto textile fabric presents other problems that have not been solved in the prior art. To cure UV ink, for example, it must be possible to precisely focus a UV curing light onto the ink. UV ink, when jetted onto fabric, particularly onto highly textured fabric, is distributed at various depths over the texture of the fabric surface. Furthermore, the ink tends to soak into or wick into the fabric. As a result, the ink is present at various depths on the fabric, so that some of the ink at depths above or below the focal plane of the UV curing light evade the light needed to cause a total cure of the ink. In order to cure, UV ink must be exposed to UV light at an energy level above a curing threshold. However, increasing the intensity of the curing light beyond certain levels in order to enhance cure of the ink can burn, scorch or otherwise have destructive effects on the deposited ink or the fabric. Furthermore, ink jet printing can be carried out with different ink color dots applied in a side-by-side pattern or in a dot-on-dot (or drop-on-drop) pattern, with the dot-on-dot method being capable of producing a higher color density, but the higher density dot-on-dot pattern is even more difficult to cure when the cure is by UV light.
In addition, UV ink can be applied quickly to reduce wicking and UV ink can be developed to allow minimized wicking. Some wicking, however, helps to remove artifacts. Further, inks developed to eliminate wicking leave a stiff paint-like layer on the surface of the fabric, giving the fabric a stiff feel or xe2x80x9cbad handxe2x80x9d. Therefore, to reduce the UV curing problem by eliminating wicking is not desirable.
UV curing of jetted ink on fabric has a limited cure depth that is determined by the depth of field of the focused curing UV light. When UV curable ink is jetted onto fabric, UV light may proceed to cure an insufficient portion of the ink. A large uncured portion of the deposited ink can cause movement or loss of the ink over time, resulting in deterioration of the printed images. Even if a sufficient portion of the ink is cured to avoid visibly detectable effects, uncured ink at some level has the possibility of producing symptoms in some persons who contact the printed fabric. The amount of uncured monomers or ink components that can cause problems by inhalation or direct skin contact has not been officially determined, but standards exist for determining limits for components of packaging material ingested with food. For example, if more than approximately 100 parts per million (PPM) of ink from packaging material is present in food, some persons who are sensitive to the uncured monomers may suffer reactions and others may develop sensitivities to the material. Such criteria assumes that 1 square inch of packaging material makes contact with ten grams of food. Thus, to interpret this criteria, it is assumed that each PPM of ink component in packaged food is equivalent to 15.5 milligrams of ink component migrating out of each square meter of packaging material into the food. While this does not provide an exact measure of the amount of uncured ink components that might be harmful to humans, it suggests that approximately 10% of uncured ink components on items of clothing, mattress covers or other fabrics with which persons may be in contact for extended periods of time, may be unacceptable.
For the reasons stated above, UV curable inks have not been successfully used to print onto fabric where a high degree of cure is required. Heat curable or other solvent based inks that dry by evaporation can be cured on fabric. As a result, the ink jet printing of solvent based inks and heat curable or air dryable solvent based ink has been the primary process used to print on fabric. Accordingly, the advantages of UV or other radiation curable ink jet printing have not been available for printing onto fabric.
There exists a need in printing of patterns onto mattress ticking and mattress cover quilts, as well as onto other types of fabrics, for a process to bring about an effective cure of ink compositions containing UV curable inks and to render practical the printing with UV curable inks onto fabric.
An objective of the present invention is to provide an effective method and apparatus for wide width xe2x80x9cdigitalxe2x80x9d or xe2x80x9csoftxe2x80x9d image printing onto textile fabric. Another objective of the invention is to effectively apply a stable curable ink onto a textile or other substrate and to effectively cure the ink on the substrate with UV other energy, a chemical curing agent or other curing medium, and particularly doing so using ink jet printing.
A further objective of the invention is to successfully apply and effectively cure ink jetted onto textiles and other substrates in a reliable manner without a tendency of the nozzles of the heads to frequently clog. Particularly, it is an objective of the invention to print onto textile fabrics and wide width substrates with a piezo or other mechanical or electromechanical print head.
Another objective of the invention is to provide for the printing onto textile fabric and other textured or wide width substrates using an ink that remains stable until deposited onto the surface of the substrate. A particular objective is to provide such a process for printing with UV ink or other inks that are curable by exposure to impinging energy. A particular objective of the invention is to provide for the effective curing of UV inks jetted onto fabric by reducing uncured monomers and other extractable non-solvent polymerization reactants, including reactant byproducts, or components of the ink, to a level most likely to be tolerable by or acceptable to persons contacting the printed substrates.
According to the principles of the present invention, a stable ink is digitally printed onto fabric and setting of the ink is initiated after the ink is deposited onto the substrate. By a xe2x80x9cstable inkxe2x80x9d is meant one that will not begin to cure, thicken or otherwise change properties in a way that will adversely affect the ability to apply the ink to the substrate, unless and until such ink is exposed to a curing medium that is otherwise absent from its environment. Inks that begin to set or which thicken upon evaporation of a solvent are not stable as herein defined. Inks that begin to polymerize before being exposed to UV light from a particular light source or to chemical agents that are provided to contact the inks after being applied to a substrate are also not considered stable.
In the preferred embodiment, stable UV ink monomers are deposited onto the substrate and polymerization of the ink is initiated by exposure to an impinged energy beam, such as UV, EB or other such energy beam. In accordance with certain aspects of the invention, the UV exposed or otherwise polymerization initiated ink is thereafter subjected to heat to reduce the content in the ink of unpolymerized polymerizable reactants and other extractable components of the ink to low levels that are likely to be tolerable or otherwise acceptable to persons contacting the fabric.
In certain embodiments of the invention, a stable ink composition is jetted onto fabric and the set or cure of the ink is initiated by exposure to a chemical substance, energy or otherwise after it is ejected from the ink jet nozzles. In the preferred and illustrated embodiments, UV polymerizable ink is jetted onto the substrate where it is exposed to UV light for its cure. Preferably, a non-bubble jet print head such as a piezo-crystal or other mechanical ink ejection transducer is used to jet the ink. Heat may be applied to the piezo-crystal or other mechanical ink injection transducer during operation, but generally only to the extent necessary for ink viscosity reduction. With or following the exposure to the UV light, the printed fabric is subjected to a heated air stream which either extends the UV light initiated curing process, drives off uncured components of the ink, or both.
Typically one or more sets of four print heads are provided on a carriage, with each of the four heads of each set configured to scan the substrate sequentially to deposit each of four colors of a CMYK color set. In a preferred embodiment, two sets of four print heads each are configured so that each set prints the same four colors in a two printhead wide strip, or alternatively, the sets are configured and controlled to print over the same area with each of eight colors.
More particularly, UV curable ink is jetted onto the fabric, and the jetted ink is exposed to UV curing light to cure the UV ink component to an extent sufficient to render the printed image substantially resistant to further wicking, which is generally about 60 to 95% polymerization depending on ink density, substrate porosity and composition, and substrate weight and thickness. Preferably, UV light curing heads are mounted on the carriage carrying the printheads across the substrate, one on each side of the heads, with the lights alternating during the bidirectional motion of the printheads to expose the ink immediately after being deposited on the substrate with light from the trailing light curing head. The light curing heads are directed onto the substrate to expose the ink immediately after it contacts the substrate to freeze the dots of ink and curtain the wicking of the ink into textile and other absorbent fabric. Then, the fabric bearing the partially cured jetted ink is heated with heated air in a heat curing oven, at which the UV light initiated polymerization may continue, or uncured monomers are vaporized, or both, in order to produce a printed image of UV ink that contains a reduced level of uncured monomers or other components of the ink which is likely to be tolerable by persons sensitive or potentially sensitive to such ink components. Preferably, the uncured components of the ink are reduced to an order of magnitude of about a gram per square meter, for example, and generally not more than about 1.55 grams per square meter of uncured monomer on the fabric substrate.
In the preferred embodiments, linear servos motors are provided to drive the print heads, at least transversely, over the substrate. Linear motors are easier to tune, require little service, and have better acceleration and deceleration than belt or other drive systems. Such servos provide accuracy that enables printing to be carried out while the heads are accelerating or decelerating. Programmed compensation is made for the variable head speed by the timing of the jetting of the ink. Thus, areas of the substrate having no printing can be skipped at high speed, greatly improving the speed and efficiency of the print operation by minimizing the time during which the print head is not depositing ink on the substrate.
According to the preferred embodiment of the invention, ink is jetted onto a textile material such as a mattress cover ticking material, preferably prior to the quilting of the fabric into a mattress cover. The ink is jetted at a dot density of about 180xc3x97256 dots per inch per color to about 300xc3x97300 dots per inch per color, though lower dot densities of from about 90xc3x97256 dots per inch or as low as about 90xc3x9790 dots per inch can be applied with acceptable resolution for certain applications. Preferably, four colors of a CMYK color palette are applied, each in drops or dots of about 75 picoliters, or approximately 80 nanograms, per drop, utilizing a UV ink jet print head. A UV curing light head is provided, which moves either with the print head or independent of the print head and exposes the deposited drops of UV ink with a beam of about 300 watts per linear inch, applying about 1 joule per square centimeter. Generally, UV ink will begin to cure, at least on the surface, at low levels of energy in the range of about 20 or 30 millijoules per square centimeter. However, to effect curing in commercial operation, higher UV intensities in the range of about 1 joule per square centimeter are desired. Provided that some minimal threshold level of energy density is achieved, which can vary based on the formulation of the ink, the energy of the beam can be varied as a function of fabric speed relative to the light head and the sensitivity of the fabric to damage from the energy of the beam.
The fabric on which the jetted ink has been thereby partially UV cured is then passed through an oven where it is heated to about 300xc2x0 F. from about 30 seconds up to about three minutes. Forced hot air may be used to apply the heat in the oven, but other heating methods such as infrared or other radiant heaters may be used. Alternatively, heated platens may be used to heat the ink bearing material, and such platens are particularly effective in bringing the material quickly up to the 300xc2x0 F. temperature. The UV energy level, oven heating temperature and oven heat time may be varied within a range of the above listed values depending on the nature of the fabric, the density, type and composition of the applied ink; and the speed of the fabric during processing relative to the UV curing light head. Thus, a higher ink density applied to the fabric will generally require more UV energy, higher oven heating temperature, longer oven heat time or a combination of these variables, to effect the necessary curing on the particular fabric.
The reliability of the printing processes may be enhanced, according to certain aspects of the invention, by preconditioning the substrate, such as by precoating, shaving or singeing of the surface to be printed. Such preconditioning eliminate dust and lint that could collect on the print heads and potentially contribute to clogging of the nozzles.
The invention further provides an online printhead cleaning station for automatic cleaning of the printheads during the course of the printing process. Preferably, periodically during the course of the printing of an extended area substrate, the printhead carriage is traversed to the printhead cleaning station where ink is jetted from the heads to purge the nozzles and the heads are wiped of ink and foreign matter that might have collected on them.
Further, the invention further provides for an ink composition which contains, in combination with the UV ink or other inks curable by exposure to impinging energy, one or more dyes which are both reactive or have an affinity to some or all of the fiber surfaces of the fabric and are compatible with the UV or other curable ink. The UV inks or other inks curable by exposure to impinging energy are comprised of a polymerizable portion and at least one pigment, suspended in the polymerizable portion.
Stable dye components can be added to the otherwise polymerizable ink to form a stable composition. The composition is digitally printed onto the substrate, whereupon the dye component is brought into contact with fiber surfaces in the fabric to chemically bond or form an affinity with those surfaces. Polymerization of the UV or other curable ink component is initiated by exposure to an impinged energy beam, such as UV, EB or other such energy beam. This effects at least a surface cure of the UV or other curable ink component, but generally has little effect on the dye component. Then the partially polymerized or cured ink is thereafter subjected to heat to both complete chemical bonding of the dye or finalizing formation of an affinity to the fiber surfaces and reduce the unpolymerized polymerizable reactants and other extractable components of the UV or other curable ink component to low levels that are likely to be tolerable or otherwise acceptable to persons contacting the fabric. Where such dye is included in the ink, the presence of heat facilitates chemical bonding or affinity formation of unreacted dye in contact with fiber surfaces in the fabric.
Where the ink composition incorporates a separate dye component which is combined with the UV or other impinging energy curable ink, the dye portion of such ink compositions may be selected from dyes that are stable and are compatible with the ink and the substrate, and are selected from the group that includes, but is not limited to, disperse dyes, reactive dyes, acid dyes, basic dyes, metallized dyes, naphthol dyes and other dyes which do not require a post-treatment to either set the dye or to develop the color. Disperse dyes are widely used for dyeing most manufactured fibers. Reactive dyes are anionic dyes which react with hydroxyl groups in cellulose fibers in the presence of alkali. Acid dyes are used on wool and other animal fibers, as well as certain manufactured fibers such as nylon. Basic dyes are positive-ion-carrying dyes which have a direct affinity for wool and silk. these dyes may also be used on basic-dyeable acrylics, modacrylics, nylons, and polyesters. Naphthol dyes are formed on the fiber by first treating the fiber with a phenolic compound in caustic solution and then applying a solution of a diazonium salt. the salt reacts with the phenolic compound to produce a colored azo compound. Generally, these dyes are used for cellulose fibers.
To the extent that a dye component is included which does not bind chemically to the fiber surfaces or form an affinity, the portion of dye which does not react with the surfaces is encapsulated within the polymerized UV ink composition to minimize migration of the dye. This encapsulation effect reduces or eliminates the need for post-treatment to remove the mobile dye from the fabric.
Further, the amount of heat needed to cause reaction or form an affinity of the dye component, when included, with the fiber surface of the fabric is a function of at least the dye component concentration, dye chemical composition, fiber composition, and fabric processing speed past or through the heat source. Generally, the upper limits for the UV or other impinging beam of energy and oven heating temperature are those values which, when applied to the specific ink and fabric, begin to damage or otherwise adversely affect the applied ink, the underlying fabric or both.
The invention has the advantage that, for different inks and using different criteria for the desired residual amount of uncured ink components remaining on the fabric, the parameters can be varied to increase or reduce the residual amount. By increasing or decreasing the intensity of energy, or using a different form of energy than UV, or by increasing or decreasing the time of exposure of the ink to the energy, the amount of remaining unpolymerized non-solvent ink components can be changed. Additionally, using higher or lower temperatures, or more or less air flow, or greater or less heating time in the post curing oven, can change the final composition of the ink on the substrate. Care, however, should be taken that the energy curing or heating process does not damage the fabric or the ink.
A further advantage of the invention is that a portion of the ink composition can be included that will combine with fiber surfaces to provide coloration which is chemically bonded or has an affinity to those surfaces. Color or wash fastness due to chemical reaction or affinity formation of the dye to fiber surfaces over at least a portion of the printed fabric is accomplished while maintaining the advantage of mechanical bonding of the UV ink component onto other portions of the fiber.
The invention makes it possible to print images on fabric with UV curable ink by providing effective curing of the ink, leaving less than a nominal 1.55 grams of uncured monomers per square meter of printed material and usually leaving only about 0.155 grams per square meter of uncured monomers. Thus, the invention provides the benefits of using UV curable ink over water and solvent based inks, including the advantages of high color saturation potential, low potential sensitivity or toxicity, and without clogging the jet nozzles and enabling the use of piezo or other high longevity print heads. Furthermore, the encapsulation effect provided by the cured UV ink substantially or completely prevents migration of non-binding dye, if included, onto other sections of the fabric, or onto other fabrics as in the case of washing the printed fabric with other items. Furthermore, the ability to print on wide width fabrics with polymerizable inks, which do not form chemical bonds with the substrates, and therefore are not material dependent, provides an advantage, particularly with fabrics such as mattress covers and other furniture and bedding products.
These and other objects of the present invention will be more readily apparent from the following detailed description of the preferred embodiments of the invention.